Scientists believe a deadly strain of the pig virus that causes 'blue-ear disease' has evolved after cases were reported this year in China and Vietnam.

China has reported losing or culling over 600,000 pigs with blue-ear disease —porcine reproductive and respiratory syndrome — since mid-2006 when this strain first appeared. Vietnam began reporting cases in March this year.

But sows and piglets are dying in the current outbreak. A group from the Institute of Microbiology in Beijing have described a genetic variation in the virus that they believe may be responsible for its increased deadliness.

Some media outlets have accused China of not sharing virus samples, but the Food and Agriculture Organization (FAO) in Beijing says this is premature, stating that it has not yet asked the Chinese government for samples or permission to investigate the outbreak, but intends to make a request soon.

The Vietnamese government has already requested assistance from the FAO after outbreaks increased in June and July. Samples are currently being analysed in US-based laboratories.